Objective: Investigate motor preparation and cognition in Parkinson’s disease (PD) patients with and without freezing of gait (FOG) while sitting and stepping with EEG.

Background: FOG pathophysiology is poorly understood but is associated motor preparation and executive deficits. Event-related potentials (ERPs) are EEG potentials in response to an event. ERPs can correlate with executive function (e.g. P3b) while others are movement-related potentials which precede voluntary movement (lateralized readiness potential (LRP)). We examine these ERPs for a simple motor task in PD with and without FOG and consider the effect of locomotion on these ERPs.

Methods: We recruited 20 PD patients (10 with FOG) to perform a two-stimulus oddball task sitting and stepping in place. Participants pressed a button once a target stimulus was seen but ignored the standard stimulus and synchronous 128-channel EEG was recorded. Response times (RTs) were calculated for sitting and stepping conditions. ERPs were calculated over centroparietal areas (for P3b responses) as well as over frontocentral areas (for LRPs).

Results: RTs while stepping were slower than while seated for the patients with FOG. However, RTs were faster while stepping for the non-freezers. In both conditions, there was no difference in the P3b ERP between groups but LRP onset is earlier in FOG, with a greater amplitude. When sitting was compared to stepping, freezers displayed an earlier onset of the LRP while stepping. There was no difference in these potentials between sitting and stepping in non-freezers.

Conclusions: This is the first study of ambulatory ERPs in Parkinson’s disease. The faster stepping RTs in the non-freezers suggests they recruit more attentional resources to perform a dual-task. The slower stepping RTs suggest the freezers are unable to do this. Although there was no difference in the P3b ERP, the longer and larger LRP implies freezers need to recruit greater frontal resources to achieve equivalent RTs to non-freezers while seated. As frontal networks become overloaded during stepping, freezers initiate movement earlier but are unable to compensate sufficiently, resulting in slower RTs.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/eeg-shows-subclinical-motor-preparation-deficits-in-parkinsons-disease-patients-with-freezing-of-gait-during-locomotion/